New research shows that a child is more likely to be diagnosed with an autism spectrum disorder (ASD) if an older sibling has already received a diagnosis.

In an international study to be published in the September 2011 issue of Pediatrics, researchers calculated the risk of recurrence among siblings. They found that number to be substantially higher than previously estimated.

Past studies had estimated the ASD recurrence risk to be between 3 percent and 10 percent. But this most recent study found that the overall risk was 18.7 percent.

The risk was even higher in families with more than one affected sibling – as high as 32 percent.

Study findings concluded that neither parental age, gender of the sibling, functioning level of the sibling, or birth order, were significant predictors of an ASD diagnosis.

Boys were found to be at nearly three times the risk of girls for an ASD diagnosis.